In the field of information recording on a recording medium and information reproduction from a recording medium on which the information is recorded, under the circumstances wherein recording and reproduction of data representing moving pictures performed with a relatively small-scale recording and reproducing instrument are desired, it is strongly required more than before to have arrangements for recording information on a recording medium with high data density, increasing data rate of information to be recorded on or reproduced from a recording medium and so on. Accordingly, with the intention of meeting such requirements, there has been proposed a multi-beam recording and/or reproducing technology for causing a plurality of light beams to be incident upon an optical recording medium on which information can be recorded with light for establishing a condition wherein information is recorded on the optical recording medium with the light beams or information recorded on the optical recording medium is reproduced form the optical recording medium with the light beams.
With the multi-beam recording and reproducing technology, advantages that the light beams such as a plurality of laser light beams are used for recording information on the optical recording medium and so that the information is recorded with high data density on the optical recording medium and the light beams are incident upon the optical recording medium independently with one another for recording information on or reproducing information from the optical recording medium so that the data rate of the information to be recorded on or reproduced from the optical recording medium is increased, are obtained. As one of information recording and reproducing apparatus, to each of which such multi-beam recording and reproducing technology as mentioned above is applied, an optical tape recording and reproducing apparatus in which a tape-shaped optical recording medium, namely, an optical tape is used, has been proposed as disclosed in the paper of “Novel digital optical tape recorder” Oakley, William S., LaserTape Inc., SPIE Proceedings Vol. 2604, pp. 256-262.
FIG. 1 shows an essential part of an example of the optical tape recording and reproducing apparatus proposed previously. In the optical tape recording and reproducing apparatus, the essential part of which is shown in FIG. 1, a laser light source 1 is provided for generating continuously a single laser light beam as a parallel light beam. The single laser light beam emitted from the laser light source 1 enters into a beam producing hologram 2.
In the beam producing hologram 2, the single laser light beam which is the parallel light beam emitted from the laser light source 1 is divided into a plurality of laser light beams each being a parallel light beam. That is, the beam producing hologram 2 is operative to produce a plurality of parallel light beams by dividing the single parallel light beam.
The laser light beams obtained from the beam producing hologram 2 enter into a polarized light beam splitter 3 and are reflected from the polarized light beam splitter 3 to be directed downward in FIG. 1 to pass through a quarter wavelength plate 4 and then enter into a converging lens 5. The converging lens 5 is operative to converge the laser light beams having passed through the quarter wavelength plate 4 to be incident upon a two-dimensional light-modulator 6.
The two-dimensional light-modulator 6 is constituted with a plurality of reflection type light-modulating elements which are arranged two-dimensionally with predetermined spaces on a common plane portion. The laser light beams from the converging lens 5 form respectively a plurality of light spots P arranged two-dimensionally with predetermined spaces on the common plane portion of the two-dimensional light-modulator 6, as shown in FIG. 2. In FIG. 2, sixty-four (8×8=64) light spots P are arranged two-dimensionally and this means that sixty-four laser light beams arranged two-dimensionally are incident upon the two-dimensional light-modulator 6.
The reflection type light-modulating elements arranged two-dimensionally with predetermined spaces on the common plane portion of the two-dimensional light-modulator 6 are positioned to correspond respectively to the light spots P formed on the common plane portion of the two-dimensional light-modulator 6 by the laser light beams incident upon the two-dimensional light-modulator 6. FIG. 3 shows an example of an arrangement of the reflection type light-modulating elements in the two-dimensional light-modulator 6. In FIG. 3, each of the reflection type light-modulating elements is represented with a rectangular parallelepiped LM and each of the light spot P is formed on the reflection type light-modulating element LM.
As shown in FIG. 4, a back surface of each of the reflection type light-modulating elements LM arranged two-dimensionally with predetermined spaces on the common plane portion of the two-dimensional light-modulator 6, which is opposite to an incident surface of the reflection type light-modulating element LM upon which one of the laser light beams is incident to form the light beam, forms a light reflecting surface RF. Therefore, the laser light beam incident upon each of the reflection type light-modulating elements LM is reflected from the light reflecting surface RF.
In relation to the two-dimensional light-modulator 6, a modulation control signal generator 7 is provided. The modulation control signal generator 7 is operative to produce a plurality of modulation control signals SM corresponding to information which are to be recorded and supply the reflection type light-modulating elements constituting the two-dimensional light-modulator 6 with the modulation control signals SM, respectively. Each of the reflection type light-modulating elements constituting the two-dimensional light-modulator 6 is operative to modulate the laser light beam which is incident thereupon and reflected therefrom in response to the modulation control signal SM. The modulation of the laser light beam in the two-dimensional light-modulator 6 is carried out by varying the reflection amount of the laser light beam at each of the reflection type light-modulating elements in response to the modulation control signal SM. Incidentally, if the modulation control signals SM require, the laser light beam which is incident upon each of the reflection type light-modulating elements constituting the two-dimensional light-modulator 6 is reflected from the reflection type light-modulating elements substantially without being modulated.
As a result of this, the laser light beams which are modulated in response to the modulation control signals SM at and reflected from the reflection type light-modulating elements arranged two-dimensionally with predetermined spaces on the common plane portion of the two-dimensional light-modulator 6, respectively, or reflected respectively from the reflection type light-modulating elements arranged two-dimensionally with predetermined spaces on the common plane portion of the two-dimensional light-modulator 6 substantially without being modulated, are obtained from the two-dimensional light-modulator 6 to be directed to the converging lens 5.
The laser light beams from the two-dimensional light-modulator 6 pass through the converging lens 5 and the quarter wavelength plate 4 to enter into the polarized light beam splitter 3. Since the laser light beams entering into the polarized light beam splitter 3 from the quarter wavelength plate 4 have passed through the quarter wavelength plate 4 twice in the direction to the converging lens 5 and in the opposite direction to the polarized light beam splitter 3, a plane of polarization of each of the laser light beams entering into the polarized light beam splitter 3 from the quarter wavelength plate 4 has been rotated by 90 degrees in comparison with that of each of the laser light beams entering into the polarized light beam splitter 3 from the beam producing hologram 2 and therefore the laser light beams entering into the polarized light beam splitter 3 from the quarter wavelength plate 4 pass through the polarized light beam splitter 3 without being reflected.
The laser light beams thus having passed through the polarized light beam splitter 3 further pass through a quarter wavelength plate 8 and a light beam control optical system 9 to be incident upon an optical tape 10 which is an optical recording medium. The light beam control optical system 9 is operative to subject each of the laser light beams passing through there to the optical tape 10 to focus control for focusing properly each of the laser light beams on the optical tape 10 and tracking control for causing each of the laser light beams to be incident upon a proper position on the optical tape 10. Further, the optical tape 10 is driven by an optical tape driving device not shown in FIG. 1 to run in the direction indicated with an allow A (hereinafter, referred as the A direction), for example.
The laser light beams passing through the light beam control optical system 9 to be incident upon the optical tape 10 form a plurality of light spots Q arranged two-dimensionally as shown in FIG. 5 on the optical tape 10. In FIG. 5, sixty-four (8×8=64) light spots Q are arranged two-dimensionally and this means that sixty-four laser light beams arranged two-dimensionally are incident upon the optical tape 10.
One of two array directions perpendicular to each other of the light spots (for example, sixty-four light spots Q) arranged two-dimensionally on the optical tape 10 is laid at an angle of α to the A direction in which the optical tape 10 runs, as shown in FIG. 5. Accordingly, with the movement of the optical tape 10 in the A direction, a plurality of recording tracks corresponding respectively to the light spots Q (for example, sixty-four light spots Q), on each of which information is recorded, are formed with a track-pitch t on the optical tape 10.
When the laser light beams which have been reflected without being modulated from the two-dimensional light-modulator 6 are incident upon the optical tape 10, these laser light beams are modulated in response to information recorded on the optical tape 10 and simultaneously reflected from the optical tape 10 to be directed to the light beam control optical system 9. The laser light beams obtained from the optical tape 10 pass through the light beam control optical system 9 and the quarter wavelength plate 8 and then enter into the polarized light beam splitter 3. Since the laser light beams entering into the polarized light beam splitter 3 from the quarter wavelength plate 8 have passed through the quarter wavelength plate 8 twice in the direction to the light beam control optical system 9 and in the opposite direction to the polarized light beam splitter 3, a plane of polarization of each of the laser light beams entering into the polarized light beam splitter 3 from the quarter wavelength plate 8 has been rotated by 90 degrees in comparison with that of each of the laser light beams entering into the polarized light beam splitter 3 from the quarter wavelength plate 4 and therefore the laser light beams entering into the polarized light beam splitter 3 from the quarter wavelength plate 8 are reflected from the polarized light beam splitter 3 to be directed to the right in FIG. 1.
The laser light beams reflected to the right in FIG. 1 from the polarized light beam splitter 3 enter into a light beam splitter 11. A part of each of the laser light beams having entered into the light beam splitter 11 is reflected from the light beam splitter 11 to be directed downward in FIG. 1 to pass through an optical element 12, such as a cylindrical lens or the like, and then enters into a focus and tracking detector 13 and another part of each of the laser light beams having entered into the light beam splitter 11 passes through the light beam splitter 11 further to pass through an optical element 14, such as a converging lens or the like, and then enters into a light detector 15.
The focus and tracking detector 13 is operative to produce output signals SF and ST which represent respectively the focus condition and the tracking condition of the laser light beams incident upon the optical tape 10 in response to the laser light beams incident upon the focus and tracking detector 13 through the optical element 12. The output signals SF and ST thus obtained from the focus and tracking detector 13 are used for the focus control and the tracking control to which each of the laser light beams passing through the light beam control optical system 9 to be incident upon the optical tape 10 is subjected.
The light detector 15 is operative to produce a plurality of output signals Sl which vary in response to variations in each of the laser light beams incident upon the light detector 15 through the optical element 14 and supply an information reproducing portion 16 with the output signals Sl. The information reproducing portion 16 is operative to reproduce the information recorded on the optical tape 10 based on the output signals Sl obtained from the light detector 15.
In the optical tape recording and reproducing apparatus thus shown in FIG. 1, when information is newly recorded on the optical tape 10, the modulation control signals SM which are produced to vary in response to the information to be recorded are supplied from the modulation control signal generator 7 to the reflection type light-modulating elements constituting the two-dimensional light-modulator 6, respectively. As the result, the laser light beams which are modulated in response to the modulation control signals SM by the reflection type light-modulating elements and simultaneously reflected from the reflection type light-modulating elements are obtained from the two-dimensional light-modulator 6 to be directed to the converging lens 5.
The laser light beams modulated in response to the modulation control signals SM and obtained from the two-dimensional light-modulator 6 pass through the converging lens 5, the quarter wavelength plate 4, the polarized light beam splitter 3 and the quarter wavelength plate 8 to enter into the light beam control optical system 9 and then are subjected to the focus control and the tracking control in the light beam control optical system 9 so as to be incident upon the optical tape 10. As a result of this, the recording of the information on the optical tape 10 is carried out with the laser light beams modulated in response to the modulation control signals SM and the recording tracks, on each of which the information is recorded, are formed on the optical tape 10.
When information recorded on the optical tape 10 is reproduced from the optical tape 10 in the optical tape recording and reproducing apparatus shown in FIG. 1, the modulation control signals SM, each of which is predetermined to be constant, are supplied from the modulation control signal generator 7 to the reflection type light-modulating elements constituting the two-dimensional light-modulator 6, respectively. As the result, the laser light beams which are reflected with a constant reflecting amount without being modulated from the reflection type light-modulating elements are obtained from the two-dimensional light-modulator 6 to be directed to the converging lens 5.
The laser light beams having not been modulated and obtained from the two-dimensional light-modulator 6 pass through the converging lens 5, the quarter wavelength plate 4, the polarized light beam splitter 3 and the quarter wavelength plate 8 to enter into the light beam control optical system 9 and then are subjected to the focus control and the tracking control in the light beam control optical system 9 so as to be incident upon the optical tape 10. The laser light beams thus incident upon the optical tape 10 are modulated in response to the information recorded on the optical tape 10 and simultaneously reflected from the optical tape 10 to be directed to the light beam control optical system 9. The laser light beams modulated in response to the information recorded on the optical tape 10 and obtained from the optical tape 10 pass through the light beam control optical system 9 and the quarter wavelength plate 8 and then are reflected from the polarized light beam splitter 3 to enter into the light beam splitter 11. The laser light beams thus entering into the light beam splitter 11 are partially reflected from the light beam splitter 11 to enter into the focus and tracking detector 13 and simultaneously partially pass through the light beam splitter 11 to enter into the light detector 15 through the optical element 14.
As a result of this, the output signal SF which represents the focus condition of the laser light beams incident upon the optical tape 10 and the output signal ST which represents the tracking condition of the laser light beams incident upon the optical tape 10 are obtained from the focus and tracking detector 13 and the output signals Sl which vary in response to variations in each of the laser light beams modulated in response to the information recorded on the optical tape 10 are obtained from the light detector 15 to be supplied to the information reproducing portion 16. Then, in the information reproducing portion 16, the information recorded on the optical tape 10 is reproduced based on the output signals Sl obtained from the light detector 15.
Further, it has been also proposed previously another optical tape recording and reproducing apparatus which uses a two-dimensional laser diode array provided therein and is different in its configuration and operation from the optical tape recording and reproducing apparatus shown in FIG. 1. FIG. 6 shows an example of a two-dimensional laser diode array 17 used for such an apparatus. In the two-dimensional laser diode array 17 shown in FIG. 6, a plurality of surface emitting laser diodes (for example, nine surface emitting laser diodes (3×3=9)) 18 are arranged two-dimensionally with predetermined space.
The two-dimensional laser diode array 17 is positioned for causing the surface emitting laser diodes 18 arranged two-dimensionally with predetermined space to face closely or come into contact with an optical tape 19, as shown in FIG. 7. When information to be recorded is newly recorded on the optical tape 19, each of the surface emitting laser diodes 18 emits a laser light beam modulated in response to the information to cause the same to be incident upon the optical tape 19. Thereby, the information is recorded on the optical tape 19.
In such a case, one of two array directions perpendicular to each other of the surface emitting laser diodes 18 arranged two-dimensionally in the two-dimensional laser diode array 17 is laid at an angle of β to the direction indicated with an allow B (hereinafter, referred as the B direction) in which the optical tape 19 runs, as shown in FIG. 8, for example. Accordingly, with the movement of the optical tape 19 in the B direction, a plurality of recording tracks corresponding respectively to the surface emitting laser diodes 18 (for example, nine surface emitting laser diodes 18), on each of which the information is recorded, are formed with a track-pitch t′ on the optical tape 19.
When the information thus recorded on the optical tape 19 is reproduced from the optical tape 19, the two-dimensional laser diode array 17 is positioned for causing the surface emitting laser diodes 18 arranged two-dimensionally with predetermined space to face closely or come into contact with the optical tape 19 on which the information is recorded and each of the surface emitting laser diodes 18 emits a laser light beam predetermined to be constant and causes the same to be incident upon the optical tape 19. The laser light beams thus incident upon the optical tape 19 are modulated in response to the information recorded on the optical tape 19 and simultaneously reflected from the optical tape 19 to return to the surface emitting laser diodes 18, respectively. Thereby, each of the surface emitting laser diodes 18 is put in an oscillating condition with the laser light beam returning thereto. Then, the oscillation in each of the surface emitting laser diodes 18 is detected to produce a detection output signal and the information is reproduced based on the detection output signals which are obtained from the surface emitting laser diodes 18, respectively.
In the optical tape recording and reproducing apparatus previously proposed as shown in FIG. 1, in which the beam producing hologram 2 and the two-dimensional light-modulator 6 are provided, the plural laser light beams which are produced by dividing the single laser light beam in the beam producing hologram 2 are incident upon the plural reflection type light-modulating elements constituting the two-dimensional light-modulator 6, respectively. Under such a situation, for establishing a condition wherein each of the plural laser light beams from the beam producing hologram 2 is incident precisely upon a corresponding one of the reflection type light-modulating elements constituting the two-dimensional light-modulator 6, it is necessary to determine and maintain rigorously positional relations among the various optical means including the beam producing hologram 2, the two-dimensional light-modulator 6 and the devices between them. However, as a matter of fact, since the reflection type light-modulating elements constituting the two-dimensional light-modulator 6 are arranged two-dimensionally with predetermined space, it is extremely difficult to determine and maintain rigorously the positional relations among the various optical means in question. Consequently, lack of necessary one or more of the laser light beams, deteriorations in coefficient of utilization of the laser light beams and so on result disadvantageously from inaccuracy in the positional relations among the various optical means in question.
Further, since one of two array directions perpendicular to each other of the light spots which are formed by the laser light beams incident upon the optical tape 10 to be arranged two-dimensionally on the optical tape 10, is laid at the angle of α to the A direction in which the optical tape 10 runs, the information recorded on the optical tape 10 to form the recording tracks are provided with phase-differences between each two recording tracks adjacent to each other. Therefore, when the information recorded on the optical tape 10 is reproduced, it is impossible to reproduce easily the information recorded on the optical tape 10 by processing the plural output signals Sl obtained from the light detector 15 in the lump and complicated signal processing for reproducing the information recorded on the optical tape 10 is required to be carried out in the information reproducing portion 16.
Then, as for the optical tape recording and reproducing apparatus using the two-dimensional laser diode array 17 provided therein and proposed previously as shown in FIG. 6, since the two-dimensional laser diode array 17 which contains the plural surface emitting laser diodes 18, each of which is operative to emit a laser light beam with very small power, for example, about 20 μW, has been merely realized, as a matter of fact, the surface emitting laser diodes 18 contained in the two-dimensional laser diode array 17 are required substantially to come into contact with the optical tape 19, as shown in FIG. 7. Therefore, the advantageous features of the optical tape recording and reproducing apparatus that noncontact information recording on and reproduction from the optical tape can be carried out so as to avoid a bad influence of extraneous substance stuck on the optical tape 19, are lost.
In addition, since one of two array directions perpendicular to each other of the surface emitting laser diodes 18 arranged two-dimensionally with predetermined space in the two-dimensional laser diode array 17 facing the optical tape 19, is laid at the angle of β to the B direction in which the optical tape 19 runs, the information recorded on the optical tape 19 to form the recording tracks are provided with phase-differences between each two recording tracks adjacent to each other. Therefore, in this case also, when the information recorded on the optical tape 19 is reproduced, it is impossible to reproduce easily the information recorded on the optical tape 19 by processing a plurality of output signals obtained from a light detector in the lump and complicated signal processing for reproducing the information recorded on the optical tape 19 is required to be carried out in an information reproducing portion.
Accordingly, it is an object of the invention disclosed in each of claims of the present application to provide an apparatus for recording information or an apparatus for recording and reproducing information, in which a plurality of light beams, such as laser light beams, are caused to be incident upon an optical recording medium, such as an optical tape, for recording information on or for recording information on and reproducing information from the optical recording medium, and with which noncontact information recording wherein information is subjected to noncontact recording on the optical recording medium or noncontact information reproduction wherein information recorded on the optical recording medium is subjected to noncontact reproduction from the optical recording medium can be carried out, difficulties in determining and maintaining positional relations among a plurality of optical means through which the light beams pass or from which the light beams are reflected can be reduced, the coefficient of utilization of the light beams can be improved, and the information recorded on the optical recording medium can be reproduced relatively easily without performing complicated signal processing.